The evolution of wireless communications has resulted in a proliferation of networks of different technologies and corresponding different air interfaces. As a result, during the course of a call, a wireless user equipment (UE) may roam among multiple radio access networks (RANs), wherein each such RAN implements a different technology than the other RANs of the multiple RANs, for example, a second generation (2G) or third generation (3G) RAN, such as a GSM (Global System for Mobile communications) RAN, a GSM/EDGE Radio Access Network (GERAN), or a UMTS Terrestrial Radio Access Network (UTRAN), that may provide primarily circuit switched voice service, and a packet data RAN, such as a later generation 3GPP LTE (Third Generation Partnership Project Long Term Evolution) network, a 3GPP2 UMB (Third Generation Partnership Project 2 Ultra Mobile Broadband) network, a WiMAX network, or a Wireless Fidelity network based on IEEE 802 standards, providing packet data Voice over Internet Protocol (VoIP) and other data related services.
The 3GPP specifications (TS 23.216) permit a UE that is engaged in a communication session via a packet data RAN and that includes a voice component, which session is anchored in an IP Multimedia Subsystem (IMS) and more particularly at a Voice Call Continuity Application Server of the IMS, to handoff the voice component from the packet data RAN to a circuit switched RAN while the call remains anchored in IMS. When the UE is a multi-radio UE that is capable of concurrent operation in both the source network and the target network, it may be possible to implement a soft handover wherein the UE exchanges bearer content with both networks in parallel during the handover. However, if the UE is a single radio UE that is capable of operation in only a single technology at any given time, then a soft handover is not possible. Currently, a scheme proposed in the 3GPP specifications for determining, by a network, whether to invoke a single radio-type handover procedure requires a single radio, SRVCC indicator to be sent to the network to invoke a single radio-type handover procedure when handing off from a packet data network to a circuit switched network. However, sending such an indicator consumes bandwidth and requires changes to the standards and software redesigns.
Therefore, a need exists for a method and apparatus for determining whether to invoke a single radio-type handover procedure when handing off a voice component of a communication session from a packet data network to a circuit switched network.